Optical system for sighting instruments



Unite States York Filed Nov. 16, 1960, Ser. No. 68,594 4 Claims. (CI. 8857) This invention relates to an optical system for sighting instruments and more particularly relates to improvements in zoom type of variable power optical systems therefor.

It is an object of this invention to provide a novel and improved zoom type of variable power optical system for sighting instruments and kindred devices wherein the image which is formed by the movable zoom lenses remains focused at a substantially stationary image position for all magnification thereof whereby the eyepiece of the instrument need not be moved coincident with changes of magnification of the instrument to maintain a correct focus thereof.

A further object of this invention is to provide such a device wherein the continuous variation of the power of a telescope is effected by two continuously and differentially moved image erecting lens members, the focal lengths or individual powers of said members being so chosen as to provide a large range of magnification of the image while achieving an excellent state of correction of all principal image aberrations, and good flatness of field.

It is a further object to provide such a device by simple and low-cost forms of optical construction but which is nevertheless reliable and is capable of high grade optical performance.

Further objects and advantages will be found in the details of construction and the combination and arrangement of parts by reference to the specification herebelow taken together with the accompanying drawing in which:

FIG. 1 is an optical diagram of a variable power telescope constructed according to our invention;

FIG. 2 is a table of constructional data related to a preferred form of our invention shown in PEG. 1; and

FIG. 3 is a graph which illustrates the differential motion of the movable zoom erector lens members.

A preferred form of our invention is incorporated in a zoom type of variable power telescope shown in FIG. 1 of the drawing. By zoom type is meant a variable power optical system which magnifies an image by continuous and uninterrupted changes of power throughout its range of magnifications of said image. Said telescope 10 comprises an objective I, a focusing lens II, a

eld lens member III, a pair of zoom or power changing erector lens members IV and V, and an eyepiece VI. All of these optical members are aligned on a common optical axis and all except member III are constructed in compound form, the elements thereof being so constructed and arranged that all of the principal image aberrations such as chromatic and spherical aberrations, coma and astigmatism as well as flatness of field are reduced to very small amounts so as to achieve a high grade of performance from the instrument throughout the range of action of the zoom lenses.

By adhering to the best procedure for devising such an optical system, the detailed design of the af resaid optical members begins with the zoom lens or erector lens section IV and V, these lenses being spaced between a fixed image point 11 and a fixed rearwardly spaced image plane 12 marked by a diaphragm 12'.

Of primary importance in this invention as well as in any zoom type of variable power optical system is the atent effecting said motions.

selection of focal lengtr s and spacings of the individual movable erector lenses IV and V which accomplih the zooming of the image without causing appreciable axial migration thereof. Optical properties of the lens system such as the range of magnification or zoom range, flatness of the image and correction of the aforesaid image aberrations are greatly benefited by a well determined distribution of lens power in the individual zoom lenses IV and V.

According to this invention by calculation and experiment the present inventors have discovered that for a range of magnification of substantially 4:1 the focal length F of the rear erector lens V should be .80F to .84F where P is the focal length of the front erector lens IV. Furthermore, the space 1 between said image point 11 and the image plane 12 should be chosen from 2.902 51 l0 Relative differential non-linear motions are provided for the erector lenses IV and V which are so designed as shown diagrammatically in FIG. 3 that the image formed by said lenses remains substantially stationary at the fixed ear image plane 12 during all changes of power or focal length of the combined erector lenses iV and V and suitable actuating mechanism (not shown) is provided for Each of the erector lenses IV and V is achromatized per se for visible light.

Lens IV is composed of a negative element IV a and a positive element lV and, similarly, lens V is composed of a positive element V a and a negative element V The focal length of the positive elements IV- and V should preferably be from .5 to .6 the focal length of their respective lens members IV and V while the negative focal length of the corresponding negative elements should be numerically between 1.10 and 1.30 of the focal length of their respective lens members IV and V. With the focal engths F and F and the distance I constructed as above specified, the air spaces preceding and following lenses IV and V should be as specified herebelow when these two lenses are jointly producing unity magnification of the image:

wherein S is the distance from the image point ll to erector lens IV, S, is the axial distance between lenses IV and V, and S is the distance between erector lens V and the image plane 12.

A further advantageous feature of this invention results from the fact that the present inventors have discovered that control of the principal ray in entering the zoom lens system IV and V can produce improvement in eye relief whereby the eyepoint remains substantially fixed in position throughout the zoom range and provide a constant apparent field. In effect, the principal ray is caused to traverse the eyepiece IV along substantially the same path for all magnifications of the zoom system. To accomplish this result, control of the principal ray is achieved by suitable design of the lens members I, II, and III and said ray is thereby introduced into the zoom lens system in such a manner that the desired control is achieved.

In accordance with the foregoing paragraph, said objective lens member I comprises a front biconvex element I and a meniscus element I spaced rearwardly therefrom at a distance S the focal length P of this combination being from 6.0F to 7.2F Preferably, the positive focal length of biconvex element I =3.OF to 3.5F and the negative focal length of meniscus element I =5.0F to 6.0F while the space S therebetween should be between .43F and .47F

Spaced rearwardly from objective I at a distance within the range S =3.9F to 4.76F is a two-part focusing lens member II which is provided to efiect internal focusing of the instrument 10 for close object distances. Said focusing member II has a negative focal length F which is preferably l.6F to 2.0F It comprises a front plano convex lens element =II having a positive focal length of substantially 1.08F and a negative lens element Il having a negative focal length of substantially .SOF I, said negative element being spaced rearwardly from lens II by a dimension of substantially .0235;;.

A field lens III is provided rearwardly of the objective I and focusing lens I-I, said lens III in cooperation with the aforesaid lenses forming a real image at a first image point 11. The focal length of the field lens III lies between LZF and LSF and it is spaced a distance of from 5.81 to 6.1 F rearwardly of said objective I. Image plane 11' is spaced rearwardly from the field lens III a distance S of substantially .34F

An eyepiece VI having a long eye relief 14 as well as other suitable optical properties which are compatible with the remaining componentparts of the telescope is focused at image plane 12 for viewing the image formed thereat.

Herebelow are given the constructional data related to one successful form of our invention and this material is also given in FIG. 2 of the drawing.

tor lenses so that a very liberal continuous range of image magnifications is afforded while still achieving an excellent state of correction of the image aberrations, all of which is in fulfillment of the objects of this invention.

Although only a preferred form of this invention has 15 been shown and described in detail, other forms are possible and changes may be made in the constructional details thereof within the stated range of values, without departing from the spirit of this invention as defined in the appended claims.

What is claimed is:

1; A zoom type of pancratic optical system for sighting instruments and the like comprising an objective member, a focusing member, a field lens, a pair of movable erector lenses for varying the magnification of the image through a range of substantially 4:1 and an eyepiece for viewing the image formed by said erector lenses, all of these lens parts being optically aligned in the order named, said L signifies lowest magnification U signifies unity magnification H signifies high magnification Table Lens Lens Radii Thick- Focal Spacings 1m 11 Group Elem. nesses Lgth.

R 103.75 a t1=l1.0 1 517 64 5 R =l49. 97 I S1=16.05

Fr +240. 82 R3 =107.65 b 82=6.0 1 7506 27 8 S2=156.9 R5 m a ta=2i5 1 689 30 9 Rs =50. 582 II Sa=1. 57

Fir -67.87 R1 =--45. 290 b t4=1 5 1 620 60 3 S4=53.6 R 29.648 III s=4-5 1 5286 51 6 R1o= l94.09

S5=l2. 4 L=35. 227 So U=25. 72

Frrr +49.0 a ia=1.6 1 7506 27 8 Ru= 15 276 IV R1s= 16. 444 b t1=4. 8 1. 612 59. 5

L=31.173 S1 U=33.064

H=3.852 Ru- 31-915 a is=4-6 1 612 59 5 at 7 R1a= 13. 183 V R11=-12.706 b to=3,0 1 7506 27 8 L=26.98 Sa U=34. 595 E=72.398

wherein: erector lenses being movable differentially With reference to a stationary image formed cooperatively by the objective member, focusing member and said field lens,

said erector lenses being located between said image and a second substantially stationary image plane formed rearwardly of and by the aforesaid erector lenses, the focal length F of the rearmost erector lens being 80% to 84% of the focal length F of the front erector lens 6 S is the axial space between lens Ill and the first focal plane following lens III. 2. An optical system for telescopes according to claim 1 wherein said erector lenses are individually achromatiand the axial distance between said image and said second 5 cally corrected and each comprises a positive element and image plane being between 2.9F and 3.0F whereby a negative element with the positive elements nearest to a magnification range of substantially 4:1 is provided for each other, the focal length of said positive elements being the instrument, the principal ray being so controlled by between .5 and .6 of the focal length of their respective the lens members ahead of the erector lenses and by the lens members and the negative focal length of said negaerector lenses that said ray traverses said eyepiece along 10 tive elements being between 1.10 and 1.30 of the focal substantially the same path during all changes of magnilengths of their respective lens members. fication, the control function being effected by a calcu- 3. A zoom type of pancratic optical system for sightlated combination of focal lengths and spacings of obing instruments comprising an objective member, a movjective I, focusing lens II, field lens III and erector lenses able focusing member located coaxially rearwardly there- IV and V, as follows: of, and a stationary field lens located rearwardly of said focusing member, the aforesaid lenses cooperating to form 6 ()F F 7,21 an image of an object at a first image plane, a pair of 1.6F -F 2 1 erecting lenses which are movable difierentially to change 1 2F F 15FIV the magnification of the image formed rearwardly there- W m of by said lenses at a second image plane, and an eye- 3.9OF S 4.76F 1 33F S 1 61F piece focused at said second image plane, the construc- IV 4 IV tional data being given in the table of values herebelow 1F IV S5 -38F IV wherein R to R are the radii of the lens elements such cessively from the front of the system, t to t are the axial w thicknesses of said elements, S to S are the axial dis- F is the focal length of the objective lens tances between the lens members, F to F are the focal F is the focal length of the focusing lens lengths of said members, n represents the refractive F is the focal length of the field lens index for the D line of the spectrum of the optical con- S is the axial space between lensI-and lens II struction materials and 1/ represents the Abbe numbers S is the axial space between lens II and lens HI 3O therefor:

Table Lens Lens Radii Thick- Focal spacings m) P Group Elem. nesses Length R1=103.75 a t1=11.0 1.517 64.5

Rg=149.97 I S1=l6.05

1 240 82 1n=-107.65 b tz=6.0 1. 7506 27.8

s,=15s.9 R =eo a t3=2.5 1. 689 30.9

R =50.582 II s1=1.57

Fri 67.87 R7=-45.2s0 b t4=1.5 1.620 60.3

Sr=53.6 RB=29.648 III 1.5286 51.6

L=35.227 s1 U=25.72

H=17.129 R11=3L9l5 FnI +490 a t5=1.6 1. 750s 27.8

Ri2=15.276 IV Ria=16.444 b t1=4.8 1.612 59.5 rv +36.3 Ri4=36.983

L =31.173 S7{U=33.064

H-3.85 R1 =3L915 a iB=4.6 1.612 50.5 Fv +29.7 R a=-l3.183 V Rl7= l2.706

n=a0 1.7506 27.8 R =26.546

L =26.98 S {U=34.595 H=72.398

wherein:

L signifies lowest magnification U signifies unity magnincation H signifies high magnification 4. A zoom type of erector for a variable power optical system for sighting instruments comprising a pair of erector lenses mounted coaxially with said system and individually movable axially differentially in such a manner as to form a substantially stationary well corrected rear image of a stationary front image at a constantly variable magnification through a magnification range of substantially '4, said front and rear images being separated by a distance which is designated by l, the focal lengths F and F of the front and rear lenses respectively being positive and being related to each other by the mathematic'al statement,

the distance I being given by the statement 2.9F l 3.0F

the variable distances 8,; between said front image and each erector lens having a positive and a negative lens element, the refractive index thereof being respectively substantially 1.612 and 1.7506.

References Cited in the file of this patent UNITED STATES PATENTS 1,091,933 Humbrecht Mar. 31, 1914 2,479,792 Tackaberry Aug. 29, 1949 2,662,443 Loeck Dec. 15, 1953 Mew 

